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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4469) Add support for user defined table function in Table API & SQL
Date Wed, 16 Nov 2016 22:50:04 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15671956#comment-15671956
] 

ASF GitHub Bot commented on FLINK-4469:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2653#discussion_r88347669
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/functions/TableFunction.scala
---
    @@ -0,0 +1,119 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.flink.api.table.functions
    +
    +import org.apache.calcite.sql.SqlFunction
    +import org.apache.flink.annotation.Internal
    +import org.apache.flink.api.common.functions.InvalidTypesException
    +import org.apache.flink.api.common.typeinfo.TypeInformation
    +import org.apache.flink.api.java.typeutils.TypeExtractor
    +import org.apache.flink.api.table.{ValidationException, FlinkTypeFactory}
    +
    +import scala.collection.mutable.ListBuffer
    +
    +/**
    +  * Base class for a user-defined table function (UDTF). A user-defined table functions
works on
    +  * one row as input and returns multiple rows as output.
    +  *
    +  * The behavior of a [[TableFunction]] can be defined by implementing a custom evaluation
    +  * method. An evaluation method must be declared publicly and named "eval". Evaluation
methods
    +  * can also be overloaded by implementing multiple methods named "eval".
    +  *
    +  * User-defined functions must have a default constructor and must be instantiable during
runtime.
    +  *
    +  * By default the result type of an evaluation method is determined by Flink's type
extraction
    +  * facilities. This is sufficient for basic types or simple POJOs but might be wrong
for more
    +  * complex, custom, or composite types. In these cases [[TypeInformation]] of the result
type
    +  * can be manually defined by overriding [[getResultType()]].
    +  *
    +  * Internally, the Table/SQL API code generation works with primitive values as much
as possible.
    +  * If a user-defined table function should not introduce much overhead during runtime,
it is
    +  * recommended to declare parameters and result types as primitive types instead of
their boxed
    +  * classes. DATE/TIME is equal to int, TIMESTAMP is equal to long.
    +  *
    +  * @tparam T The type of the output row
    +  */
    +abstract class TableFunction[T] extends UserDefinedFunction with EvaluableFunction {
    +
    +  private val rows: ListBuffer[T] = new ListBuffer
    +
    +  /**
    +    * Emit an output row
    +    *
    +    * @param row the output row
    +    */
    +  protected def collect(row: T): Unit = {
    +    // cache rows for now, maybe immediately process them further
    +    rows += row
    +  }
    +
    +
    +  @Internal
    +  def getRowsIterator = rows.toIterator
    +
    +  @Internal
    +  def clear() = rows.clear()
    +
    +  // this method will not be called, because we need to register multiple sql function
at one time
    +  override private[flink] final def createSqlFunction(
    +      name: String,
    +      typeFactory: FlinkTypeFactory)
    +    : SqlFunction = {
    +    throw new UnsupportedOperationException("this method should not be called")
    --- End diff --
    
    Why is this method not necessary for `TableFunction`?


> Add support for user defined table function in Table API & SQL
> --------------------------------------------------------------
>
>                 Key: FLINK-4469
>                 URL: https://issues.apache.org/jira/browse/FLINK-4469
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Jark Wu
>            Assignee: Jark Wu
>
> Normal user-defined functions, such as concat(), take in a single input row and output
a single output row. In contrast, table-generating functions transform a single input row
to multiple output rows. It is very useful in some cases, such as look up in HBase by rowkey
and return one or more rows.
> Adding a user defined table function should:
> 1. inherit from UDTF class with specific generic type T
> 2. define one or more evel function. 
> NOTE: 
> 1. the eval method must be public and non-static.
> 2. the generic type T is the row type returned by table function. Because of Java type
erasure, we can’t extract T from the Iterable.
> 3. use {{collect(T)}} to emit table row
> 4. eval method can be overload. Blink will choose the best match eval method to call
according to parameter types and number.
> {code}
> public class Word {
>   public String word;
>   public Integer length;
> }
> public class SplitStringUDTF extends UDTF<Word> {
>     public Iterable<Word> eval(String str) {
>         if (str != null) {
>             for (String s : str.split(",")) {
>                 collect(new Word(s, s.length()));
>             }
>         }
>     }
> }
> // in SQL
> tableEnv.registerFunction("split", new SplitStringUDTF())
> tableEnv.sql("SELECT a, b, t.* FROM MyTable, LATERAL TABLE(split(c)) AS t(w,l)")
> // in Java Table API
> tableEnv.registerFunction("split", new SplitStringUDTF())
> // rename split table columns to “w” and “l”
> table.crossApply("split(c) as (w, l)")	
>      .select("a, b, w, l")
> // without renaming, we will use the origin field names in the POJO/case/...
> table.crossApply("split(c)")
>      .select("a, b, word, length")
> // in Scala Table API
> val split = new SplitStringUDTF()
> table.crossApply(split('c) as ('w, 'l))
>      .select('a, 'b, 'w, 'l)
> // outerApply for outer join to a UDTF
> table.outerApply(split('c))
>      .select('a, 'b, 'word, 'length)
> {code}
> See [1] for more information about UDTF design.
> [1] https://docs.google.com/document/d/15iVc1781dxYWm3loVQlESYvMAxEzbbuVFPZWBYuY1Ek/edit#



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